Study of intense femtosecond laser propagation into a dense Ar gas and cluster jet.

The propagation of an intense (up to 1017 W/cm2) and short laser pulse (down to 40 fs) is studied through a well characterized high density Ar cluster jet obtained at the output of a supersonic nozzle. The x-ray emission from the irradiated clusters is measured as a function of the focusing depth inside the jet, with a spatial resolution of the emitting plasma. A strong refraction of the laser pulse is observed, limiting the interaction at the entrance of the jet and decreasing the effective laser intensity on clusters. Calculations indicate that it is due to the ionization of the residual gaseous phase present in the cluster jet. As the focal volume is modified, this effect should be considered for any quantitative analysis of the laser-cluster interaction. [ABSTRACT FROM AUTHOR]